High-resolution HLA-DRB typing is required for bone marrow transplantation between unrelated donors and recipients and also for identification of novel HLA-DRB alleles. The highly variable second exon of all HLA-DRB1, -DRB3, -DRB4, -DRB5, -DRB6 and -DRB7 alleles was amplified using a single pair of generic DRB-specific primers and alleles were separated by DGGE. DNA was then reamplified from plugs removed from the gel and the sequences of these alleles were determined using fluorescent-based sequencing and allele-assignment software. RESULTS The validity of this typing procedure was confirmed by identification of HLA-DRB alleles for 17 individuals previously characterized by PCR-SSP and/or cloning and sequencing techniques. We identified 34 different HLA-DRB alleles in these 17 unrelated individuals. Our analysis revealed HLA-DRB1 alleles which had not been identified using the PCR-SSP typing technique. Additionally, alleles from the HLA-DRB3, -DRB4 and -DRB5 loci were identified. Whereas traditional HLA-DRB typing methods provide limited information or require the use of multiple oligonucleotide primers or probes, our technique provides a reliable, specific and relatively rapid way of identifying all HLA-DRB alleles for high-resolution tissue typing. OBJECTIVE: To describe a method for the unambiguous identification of HLA-DRB alleles using the polymerase chain reaction (PCR), denaturing gradient gel electrophoresis (DGGE) and direct FUTURE DIRECTIONS This technique can now be used to define the DRB1 alleles of patients undergoing bone marrow transplantation. KEY WORDS cross-reactivity, DGGE, DNA, HLA-DRB, PCR, sequencing, typing